The present invention relates to the field of communication networks, and, more particularly, to mobile ad hoc wireless networks and related methods.
Wireless networks have experienced increased development in the past decade. One of the most rapidly developing areas is mobile ad hoc networks. Physically, a mobile ad hoc network includes a number of geographically-distributed, potentially mobile nodes wirelessly connected by one or more radio frequency channels. Compared with other type of networks, such as cellular networks or satellite networks, the most distinctive feature of mobile ad hoc networks is the lack of any fixed infrastructure. The network is formed of mobile nodes only, and a network is created on the fly as the nodes transmit to or receive from other nodes. The network does not in general depend on a particular node and dynamically adjusts as some nodes join or others leave the network.
In a hostile environment where a fixed communication infrastructure is unreliable or unavailable, such as in a battle field or in a natural disaster area struck by earthquake or hurricane, an ad hoc network can be quickly deployed and provide much needed communications. While the military is still a major driving force behind the development of these networks, ad hoc networks are quickly finding new applications in civilian or commercial areas. Ad hoc networks will allow people to exchange data in the field or in a class room without using any network structure except the one they create by simply turning on their computers or PDAs.
As wireless communication increasingly permeates everyday life, new applications for mobile ad hoc networks will continue to emerge and become an important part of the communication structure. Mobile ad hoc networks pose serious challenges to the designers. Due to the lack of a fixed infrastructure, nodes must self-organize and reconfigure as they move, join or leave the network. All nodes could potentially be functionally identical and there may not be any natural hierarchy or central controller in the network. Many network-controlling functions are distributed among the nodes. Nodes are often powered by batteries and have limited communication and computation capabilities. The bandwidth of the system is usually limited. The distance between two nodes often exceeds the radio transmission range, and a transmission has to be relayed by other nodes before reaching its destination. Consequently, a network has a multihop topology, and this topology changes as the nodes move around.
The Mobile Ad-Hoc Networks (MANET) working group of the Internet Engineering Task Force (IETF) has been actively evaluating and standardizing routing, including multicasting, protocols. Because the network topology changes arbitrarily as the nodes move, information is subject to becoming obsolete, and different nodes often have different views of the network, both in time (information may be outdated at some nodes but current at others) and in space (a node may only know the network topology in its neighborhood usually not far away from itself).
A routing protocol needs to adapt to frequent topology changes and with less accurate information. Because of these unique requirements, routing in these networks is very different from others. Gathering fresh information about the entire network is often costly and impractical. Many routing protocols are reactive (on-demand) protocols: they collect routing information only when necessary and to destinations they need routes to, and do not generally maintain unused routes after some period of time. This way the routing overhead is greatly reduced compared to pro-active protocols which maintain routes to all destinations at all times. It is important for a protocol to be adaptive. Ad Hoc on Demand Distance Vector (AODV), Dynamic Source Routing (DSR) and Temporally Ordered Routing Algorithm (TORA) are representative of on-demand routing protocols presented at the MANET working group.
Examples of other various routing protocols include Destination-Sequenced Distance Vector (DSDV) routing which is disclosed in U.S. Pat. No. 5,412,654 to Perkins, and Zone Routing Protocol (ZRP) which is disclosed in U.S. Pat. No. 6,304,556 to Haas. ZRP is a hybrid protocol using both proactive and reactive approaches based upon distance from a source node.
These conventional routing protocols use a best effort approach in selecting a route from the source node to the destination node. Typically, the number of hops is the main criteria (metric) in such a best effort approach. In other words, the route with the least amount of hops is selected as the transmission route.
Existing communication node advertisement and communication node neighbor discovery approaches including those for ad hoc networks, only use network-condition-independent mechanisms such as constant transmit rate or random transmit rate xe2x80x9chelloxe2x80x9d messages from nodes to announce, or advertise, their presence. These transmitted announcements are called xe2x80x9cbeaconsxe2x80x9d and under conventional approaches, these beacons are not endowed with any degree of intelligence. Other nodes may detect these beacons and either form a network from scratch or add the newly-detected node to the existing network.
In view of the foregoing background, it is therefore an object of the present invention to provide the xe2x80x9cIntelligent Communication Node Object Beacon Frameworkxe2x80x9d (ICBF), for intelligent, adaptive advertisement by any communications node object of its presence along with the management and control of route discovery and associated processes via temporal transitioning processes and events in a mobile ad hoc network.
This and other objects, features, and advantages in accordance with the present invention are provided by a method for managing and controlling the discovery and maintenance of routes in a mobile ad hoc network. The network includes a plurality of mobile nodes and a plurality of wireless communication links connecting the nodes together. The method includes transmitting beacon signals from each mobile node, determining a node or group condition at each mobile node, and varying the beacon signals based upon the determined node/group condition. Also route tables are bulit and updated at each mobile node with a first one of proactive and reactive route discovery processes to define routes in the network. A route is a set of wireless communication links and mobile nodes from a source to a destination. The beacon signals are received and node/group condition information is stored at each node. Route stability over time is predicted based upon the node/group condition information, and when predicted route stability reaches a first transition parameter the method switches to a second one of the proactive and reactive route discovery processes.
The method preferably includes switching back to the first one of the proactive and reactive route discovery processes when predicted route stability reaches a second transition parameter, and the first and second transition parameters preferably specify time-dependent conditions. Varying the beacon signal may comprise varying at least one of transmission rate, transmission frequency and transmission pattern. Also, the transmission rate of the beacon signal should not exceed a rate threshold based upon available bandwidth.
The node/group condition may include node/group movement, and varying the beacon signal may comprise increasing the transmission rate based upon increased node/group movement and decreasing the transmission rate based upon decreased node/group movement. Node/group movement comprises at least one of node/group velocity, node/group acceleration and node/group movement pattern of the corresponding mobile node or group of mobile nodes. Node/group condition information is based upon node mobility, link failure, link creation, node/group stability and link quality, and storing node/group condition information may comprise creating and updating a time-dependent route stability profile. Furthermore, storing node/group condition information may also include creating and updating a time-dependent route segment stability profile. A segment is a set of links and nodes which define a reusable entity in one or more routes.
A mobile ad hoc network according to the present invention includes a plurality of mobile nodes, and a plurality of wireless communication links connecting the mobile nodes together. Each mobile node include a communications device to wirelessly communicate with other nodes of the plurality of nodes via the wireless communication links, and a controller to route communications via the communications device. The controller has a condition determining unit to determine a condition of the mobile node or group of nodes, and a beacon signal generator to generate and transmit beacon signals. The beacon signal generator varies the beacon signals based upon the determined condition of the mobile node/group.
Route tables define routes in the network. A route is a set of wireless communication links and mobile nodes from a source to a destination. The controller also includes a route discovery module to discover routes and update the route tables with one of a plurality of route discovery processes, a condition module to receive beacon signals and store node/group condition information, a route stability predictor to predict route stability over time based upon the node/group condition information, and a route discovery process selector to select between the plurality of route discovery processes based upon the predicted route stability.